Bactericidal agents are used extensively in all areas such as engineering, cosmetics, food processing, pharmaceuticals, agriculture, and dairy husbandry. The types of bactericidal agents are quite versatile and examples used in medical and food fields include chlorine sterilizers, iodine sterilizers, peroxide sterilizers, aldehyde sterilizers, phenolic sterilizers, biguanide sterilizers, mercury sterilizers, alcoholic sterilizers, quaternary ammonium salt sterilizers, and amphoteric surfactant sterilizers.
However, most of these sterilizers suffer considerable drop in bactericidal power in the face of contaminating by organic substances such as proteins or in the presence of biofilms covered with polysaccharides or proteins. This leads to a discrepancy between bactericidal evaluation in the laboratory and on-site evaluation and the resulting failure to inhibit bacterial growth and eventually causes infection. Particularly notable in this respect are biofilms which can sometimes pose serious problems both in the living environment of humans and in the industry. Take, for example, a dwelling environment; biofilms can be a cause of discomfort if they produce slimes, clogging or malodor in toilets, kitchens, bathrooms, etc. Another potential cause of infections is the bacteria in biofilms formed in water-circulating bathtubs in hot spa facilities and the like. Problems are also encountered in industrial fields, as exemplified by corrosion from biofilms that are formed on the inner surfaces of sewage pipes and on ship bottoms; biofilms on production lines in plants can be another cause of microbial contamination. In medical-related areas, biofilms formed in tubes for dialysis and other applications, as well as in medical devices such as endoscopes and contact lenses can be a source of infection; diseases can also be caused by biofilm formation in skin and other human tissues. In the human oral cavity, it is well known that biofilms formed on teeth which are commonly called “dental plaques” can cause dental caries and periodontal disease. In food-related areas, biofilms formed on perishable goods such as vegetables, as well as materials for processed foods and cooking utensils are potential causes of putrefaction and food poisoning. These problems are currently coped by specifying bactericidal concentrations for actual use that are much higher than those found in the laboratory.
It was proposed that penetrability into biofilms be improved by methods characterized by additional use of anionic surfactants (Patent Documents 1, 2 and 3). These known techniques, however, had their own problems. For example, in actual use, contaminating by organic substances is assumed and bactericidal concentrations are specified that are much higher than those found in the laboratory; however, even such higher concentrations were unable to kill the bacteria found in excessive contaminations or biofilms and, what is more, they were undesirable from the viewpoints of human body and environmental safety. Another problem was that fatty acid esters of glycerol which would not lose bactericidal or antibacterial activity in the contamination by organic substances had no antibacterial activity against Gram-negative bacteria (Non-Patent Document 1). To deal with this problem, it was proposed that ethylenediaminetetraacetic acid, a chelatant having bactericidal power against Gram-negative bacteria, be additionally used to make up for the disadvantage of fatty acid esters of glycerol (Patent Documents 4, 5 and 6); however, ethylenediaminetetraacetic acid had a problem with the latitude of formulation in that only limited combinations of formulations was permitted, as exemplified by the case where it reacted with hypochlorous acid or salts thereof and the available chlorine concentration decreased to result in a lower bactericidal power. As already mentioned, it was proposed that penetrability into biofilms be improved by methods characterized by additional use of anionic surfactants (Patent Documents 1, 2 and 3) but they also had a problem with the latitude of formulation, as exemplified by the attenuation of bactericidal power due to an electrical interaction that occurred when they were used in combination with cationic sterilizers.